Production of artificial fibers



April 1937- A. FORMHALS 2,077,373

PRODUCTION OF ARTIFICIAL FIBERS Filed Aug. 15, 1936 T 15 FIG. 3. WSW

' Lin-l 1X1 LEIYTOR.

Patented Apr. 13, 1937 UNITED STATES PATENT OFFICE PRODUCTION OF ARTIFICIAL FIBERS Application August 15, 1936, Serial No. 96,226 In Germany November 30, 1934 Claims.

This invention relates to the production of artificial fibers, and more particularly, it relates to the passing of a spinning solution through a novel spinneret or nozzle structure. The invention has 5 particular utility in processes for the dispersion or shattering of streams of spinning solutions into comparatively fine fibers by means of a high electrical potential. The dispersion of a stream of spinning solution into fibers by a high electrical potential shall hereinafter, for convenience, be referred to as the electrical spinning of fibers.

Spinnerets known prior tothe present invention were generally constructed by forming, such as by drilling, extremely fine openings in a plate of a comparatively hard metal alloy. Despite the fact that the spinneret plate which contains the openings have been made very thin, the ratio between the diameter of the openings and the thickness of the plate has always been very considerably less than 1:1. Such spinneret openings, therefore, consisted of cylindrical holes, the diameters of which were considerably smaller than the depth thereof. Openings in previously known spinnerets have sometimes been made of slightly conical or tapered contour, nevertheless, the diameters of such openings were also always made many times smaller than the depth thereof.

It has now been found that the openings of previously known spinnerets, whether they are of uniform cross-section or slightly tapered or conical in cross-section, are relatively easily stopped or plugged due to the relatively great length or depth thereof as compared with their diameters. The low velocity of the spinning solution adjacent the capillary walls of previously known spinneret openings, tends to cause a slow and irregular fiow of spinning solution therethrough. The low velocity of the spinning solution adjacent the walls of these openings is due to the clinging of the solution to the said walls. Furthermore, when spinning with solutions such as, for example, cellulose acetate, containing volatile solvents, the solvents tend toevaporate at the orifice or mouth of the openings, tending to congeal and form lumps at the orifice. The congealed spinning solution at the orifice adjacent the walls of the opening will not be properly removed by the stream of solution due to the low velocity of the 50 solution adjacent the walls, and, as a result, the

openings will soon become plugged.

The above defects in previously known spinnerets are particularly annoying in the manufacture of artificial fibers by means of electrical spinning processes, due to the fact that the fibers are not drawn from the nozzle orifice as in the case of other spinning processes and, because in this case, the uniform extrusion of spinning solution is an absolute necessity for uniform formation and deposition of fibers on the collecting device.

Previously known types of spinnerets, when used in the electrical spinning of fibers, are also objectionable due to the fact that the various parts of the spinnerets are held in place by means of thumb nuts or other devices which have 0 sharp corners or protrusions. When such spinnerets and holders are used in connection with electrical spinning processes, very high potentials are necessary to cause the proper breaking upof streams of the spinning solution. When such 15 very high potentials are used, a considerable portion of the formed fibers fiy back to the spinneret and interfere with the continuity of spinning.

It is therefore an object of the present invention to provide a nozzle construction which has a 20 lesser tendency to plug due to incompletely dissolved solids in the spinning solution.

It is another object of this invention toprovide a nozzle construction which will not plug or cause a decrease in solution fiow due to evaporation of r solvent from the spinning solution and drying of the spinning solution at or near the nozzle orifice.

It is a further object of the present invention to provide a nozzle which will have the property of extruding a liquid stream immediately at the 30 beginning of the operation thereof without the formation of droplets at the nozzle orifice which will necessitate wipings of the nozzle face.

It is a still further object of the present invention to provide a nozzle structure in which any 35 electrical charges applied thereto will be concentrated at the point of outflow of the spinning solution.

Other objects of the invention will appear hereinafter. 40

The object of the invention will be accomplished in general, by forming a nozzle in which the external walls converge to a somewhat pointed nozzle face, the nozzle face which comprises an orifice plate having a thickness less than the diameter of the orifice opening.

In order to more clearly set forth the present invention, reference is made to the following detailed description taken in connection with the accompanying illustration, in which, Figure 1 is an exploded sectional view of a nozzle constructed in accordance with the present invention.

Figure 2 is a highly magnified sectional view of a portion of a nozzle orifice plate.

Figure 3 is a highly magnified sectional view of a portion of a modified form of a nozzle orifice plate.

Referring to the drawing, reference numeral 8 designates one section of a demountable nozzle which is provided with internal threads ID by means of which it may be fastened to a conduit leading from a spinning solution container (not shown). The nozzle section 8 is further provided with external threads II by means of which it may be connected to nozzle section 9. The nozzle section 9 is provided with internal thread [2 for cooperation with threads H whereby sections 8 and 9 may be securely fastened to each other. The section 9 is provided with a plate M, which plate may be integral with section 9 or may be a separate element fastened thereto. The plate I4 is provided with an orifice I5. As will be noted from the drawing, the gen eral outline or contour of the nozzle is such that the external walls thereof converge toward the face thereof, and if an electrical charge of high potential is imparted thereto, the charge will be collected or concentrated at the orifice plate I 4 due to the fact that orifice plate I4 constitutes an end of the projecting section 9. Referring to Figure 2 of the drawing, it will be noted that the plate !4 is made of such an extremely thin cross section T that the cross section of the plate is materially less than the diameter D of the orifice opening. It has been found that if this ratio between the diameter of the orifice opening D and the thickness of the plate T is maintained greater than 1:1, the defects of previously known spinnerets will be materially overcome. A stream of spinning solution which is passed through an orifice of the type illustrated in Figure 2 of the drawing will not exhibit the low velocity adjacent the walls thereof, such as is found in spinnerets known heretofore. As a consequence, any con- 40 gealed spinning solution at the orifice will be properly removed by the stream of solution due to its high velocity adjacent the walls thereof.

Referring to Figure 3 of the drawing, the orifice I5 is shown as not only having a greater diameter than the thickness of the plate H but has the additional feature of being countersunk from the inside to the outside of the plate M. This particular structure is the applicants preferred construction and has certain advantages over the structure as shown in Fig. 2. By constructing the nozzle opening in such a manner that the diameter D will be greater than the thickness of the plate I4, and at the same time constructing the opening with a sharp taper towards the bottom of the nozzle face, the velocity adjacent the walls of the orifice will be substantially as great as the velocity at the center of the orifice. Therefore, any congealed spinning solution which may adhere to the mouth of the opening l5 will be removed due to the velocity of the spinning solution. Furthermore, by constructing the orifice plate in the manner described, it will have particular utility in the production of fibers by the electrical spinning processes in which the stream of spinning solution is not drawn from the nozzle orifice as in the case of ordinary stretch spinning processes. The spinning solution is forced from the orifice opening by means of pressure applied to the spinning solution and therefore, difficulty has been experienced heretofore, by the formation of droplets at the mouth of the orifice when the pressure is first applied to the spinning solution. In the construction illustrated in Figure 3 of the drawing, however, due to the extremely thin and sharp edge of the point of outflow of the spinning solution a stream vwill immediately form without first forming an objectionable droplet at the mouth thereof.

A nozzle constructed in accordance with the present invention is particularly desirable in the electrical spinning of fibers by reason of the fact that it will continuously produce a single stream of spinning solution having a uniform cross section and speed. The stream will be shattered by the electrical charge to produce a constant flow of finely divided fibers which are of substantially uniform cross section.

Obviously, many changes and modifications may be made in the construction of the nozzle as above described without departing from the nature and spirit of the invention. It is therefore to be understood that the invention is not to be limited thereto except as set forth in the appended claims.

I claim:

1. In anozzle for the electrical spinning of artii imparted thereto will be concentrated at said plate.

2. In a nozzle for the electrical spinning of artificial fibers, a face plate, a single outlet opening in said plate, the diameter of said opening being greater than the length thereof, said opening conically converging from the internal surface of said plate towards the external surface thereof.

3. In a nozzle for the electrical spinning of artificial fibers, a face plate, an outlet opening in said plate, the diameter of said opening being greater than the length thereof, said opening conically converging from the internal surface of said plate towards the external surface thereof, in such a manner as to form an extremely thin, sharp edged outlet orifice.

4. In a nozzle for the electrical spinning of artificial fibers, a face plate, an outlet opening in said plate, the diameter of said opening being greater than the length thereof, said opening conically converging from the internal surface of said plate towards the external surface thereof, said nozzle having such an external outline that any electrical charge imparted thereto will be concentrated at said face plate.

5. ha method for the electrical spinning of fibers, the step which comprises passing a spinning solution through an outlet opening of a nozzle which opening has a greater diameter than length.

ANTON FORMHALS. 

